Permanent magnet yoke



April 29, 1958 DE FOREST 2,832,922

PERMANENT MAGNET YOKE Filed Feb. 14, 1955 L9 W" h 5a r" W W 4 1 WM. 4% Z4 5 Z3 Z4 1: 25 24 i g l I I l i 1 Z5, 4 23 4g 1, 52

Taber ae FbreSi United States Patent PERMANENT MAGNET YOKE Taber De Forest, Northiorook, Ill., assignor to Magnaflux Corporation, Chicago, 311., a corporation of Deiaware Application February 14, 1955, Serial No. 488,072

2 Claims. (Cl. 317--203) tomary to employ electromagnetic means for magnetizing the test piece, or work. However, in the case of relatively small articles or where the work piece to be tested is relatively inaccessible, it is desirable to have a portable source of magnetization that can be manually adjusted and positioned so as to straddle the area to be tested. I have now developed for this purpose a jointed permanent magnet yoke of light weight and simple construction and having a substantial universality of adjustment with respect to the permanent magnet pole pieces.

It is therefore an'important object of this invention to provide a jointed permanent magnet yoke having the above mentioned features of adjustability that render it particularly adaptable in the magnetic particle inspection of articles and the like capable of being magnetized.

It is a further important object of this invention to provide a relatively inexpensive and simple construction of a permanent magnet assembly wherein the pole pieces are capable of a considerable degree of adjustability with respect to one another and means are provided for releasably holding the pole pieces in their adjusted position.

Other and further important objects of this invention will become apparent from the following description and appended claims.

For a more specific explanation of one form of the invention, reference is made to the attached sheet of drawings, in which:

Figure l is a front elevational view of a jointed permanent magnet yoke embodying the principles of my invention.

Figure 2 is an enlarged view of the same in another position, with parts broken away and in section.

Figure 3 is an end elevational view with parts broken away and in section.

Figure 4 is a further enlarged sectional detail view, partly broken away, illustrating features of adjustability.

On the drawings:

The reference numeral indicates generally a permanent magnet yoke embodying the principles of my invention. Said yoke comprises a jointed assembly including an intermediate portion 11, which may serve as a handle and which is here shown as comprising a pair of relatively elongated plates 12 and 13 of identical cross section but reversed when assembled. The plates 12 and 13 are arranged in spaced-apart parallel relationship for receiving therebetween at each end a slightly offset arm 14. Each arm 14 has a flattened end 15 which extends between the plates 12 and 13 and against the plane surfaces of which said arms 12 and 13 are resiliently held for relative pivotal movement. In order to provide for V, 2,832,922 Patented Apr. 29, 1958 fin? such pivotal movement, each of the flattened ends 15 is provided with an internally threaded, transversely extending through bore 16, and the plates 12 and 13 are provided with countersunk bores 17 and 18 for alignment with said bore 16. Threaded bolts 19 and 20, provided with spring washers 21 and 22, are adapted to be threaded into said bores 17 and 18 so that their shanks extend in opposed relationship into the through bore 16 and th heads of said bolts lie flush within the respective counterbores of said bores 17 and 18. With said bolts 19 and 20 positioned as shown in Figure 3, the spring washers 21 and 22 are under the desired amount of compression to permit relative sw-ivelling movement of arms 14 with respect to the handle portion 11, yet with sufficient resistance to such movement to insure that said legs will remain in any relative position to which they may be adjusted.

The free ends of the arms 14 are generally cylindrical in shape, as at 23, for connection to cylindrical permanent magnets 24. Said permanent magnets may be of any high energy product type of material, such as Alnico V. Pole pieces 25 extend from the free ends of the permanent magnets 24 and are swivelly connected thereto and to the arms 14 in a manner that will now be described.

Each of the cylindrical ends 23 of the arms 14 is provvided with an axially extending bore 26, which is blind at one end and which has an enlarged portion 27 open at the end face 28 (Fig. 4) of each cylindrical arm portion 23. The bores 26 and 27 are unthreaded and are coaxial. Transverse small bores 29 extend through the cylindrical portions 23 diametrically thereof to intersect the bores 26. These bores 29 are likewise unthreaded. In addition, small diameter bores 30 extend transversely through the lower portions of the cylindrical arm portions 23 into the enlarged bores 27. The bores 30 are threaded for receiving set screws 31.

Each pole piece 25 has an axially extending blind bore 32 opening through its plane face 33, and a transversely extending bore 34 extending into the bore 32 from 9. cylindrical surface of said pole piece. Each of the bores 32 and 34 is internally threaded. A swivel pin 35 having a lower threaded end is threaded into each bore 32, and a set screw 36 is threaded into each transverse bore 34 against said lower threaded end 32 of the pin 35 to hold said pin 35 against relative rotation with respect to the corresponding pole piece 25.

After assembling its swivel pin 35 upon a pole piece 25, the corresponding permanent magnet 24 is slipped over the swivel pin while the same is held in vertical upright position. With a permanent magnet 24 so positioned and bottomed against the plane surface 33 of the corresponding pole piece, a retainer 37 is positioned on the swivel pin 35 to rest against the upper surface of the magnet 24, and then a spring washer 38 is positioned on the swivel pin 35 against the retainer 37, and, finally, a retainer nut 39 is threaded onto the upper threaded end 40 of the swivel pin 35 against said spring washer 38 but not so as to exert any compression thereagainst. Next, with the set screws 31 threaded out so as not to obstruct the enlarged bore 27, the upper end of each swivel pin 35 with its assembled elements is inserted into the bore 27 and up into the bore 26 of the arm 14 with which the swivel connection is to be made. The making of the connection is facilitated by the fact that the retainer 39 is of slightly smaller diameter than the smaller bore 26 so as to fit loosely therein, as is also the spring washer 38, and the retainer '37 is slightly smaller in diameter than the larger bore 27 to fit closely therein. Since the retainer 37 is unthreaded both internally and externally, it is necessary to secure it in place within the bore 27, and this is accomplished by turning in the set screws 31 until their inner ends project into the sockets 41 provided for the purpose (Fig. 4).

The retainer nut 39 is provided with an internally threaded through bore 42 for receiving short set screws 43 of the type adapted to receive an Allen wrench With the through bore 42 aligned with the through bore 29 in an arm 23, the Allen set screws 43 are threaded into the opposite ends of said through bore 42 until said set screws have been turned tightly up against the threaded end 49 of the swivel pin 35. At this point. the set screws 43 being of a predetermined length, lie wholly within the external cylindrical face of the retainer nut 39. Consequently, if the Allen Wrenches 44 are now withdrawn, the retainer nut 39, while secured to the threaded end 46 of the swivel pin 35, is nevertite?- to move axially relative LU inc retainer 37.

It is this relative movement that makes possibie the adjustment of the swivel connection to give the proper resistance between the elements to reltaive turning movement. With the Allen wrenches 44' in place, as shown in Figure 4, to resist relative turning movement betwce the threaded end 49 and the. retainer nut 39', and with the set screw 35 threaded home against the lower threaded end 32 of said swivel pin 35' so as to prevent relative turning movement between said threaded end 32 and the corresponding pole piece 25, the pole piece, as a whole, is turned in a direction to thread the threaded end 46 into the retainer nut 39 and thus exert a compressive or squeezing action upon the spring washer 38. When the desired amount of compression has been placed upon each spring washer 3% to elfect the desired degree of frictional resistance to relative turning movement between the abutting plane surfaces including the surfaces 28 and 33, the Allen wrenches 4 3 are then removed to leave the retainer nut 39 held by the small set screws 42 on each threaded end it? of a swivel pin 35. As iliustrated in Figure 2, the unthreaded outer portions of the through bore 2? in each of the lower arm portions 23- are left open. This facilitates the use of Allen wrenches again in case some further adjustment is desired.

Each of the pole pieces is provided with a bevelled or tapered plane surface which may be at any suitable angle to the axis of the pole piece but is here shown as at an angle of about 45. The purpose of providing sloping end faces 45 on the pole pieces 25 is. to permit greater adjustability, while at the same time insuring flat surface contact between the plane surfaces 45 and a work piece, provided that the work piece has substantially flat surfaces. As illustrated in Figure 1., the end faces 55 of each of the pole. pieces 25 are in flat surface contact with the upper surface of a strip 36, which may be considered as a work piece or the equivalent of a work piece. In order to make such fiat contact possible between the faces of the pole pieces and the surface of the work piece, it is usually necessary, or may be necessary, to pivot the arms 14, or one of them, about the ends of the handle 12 either to spread or contract the span of the assembled yoke. In addition, of course, the pole pieces 25, or either of them, can be swivelled about its own axis, as defined by the corresponding swivel pin 35, to rotate such pole piece until satisfactory surface contact has been obtained with the work piece. By a combination of the adjusting movements just referred to, either angular with respect to the intermediate or handle portion 11 or rotational about the axes of the swivel pins 35, a substantial universality of adjustability can be realized.

One of the advantages derived from the use of my jointed permanent magnet yoke is that the yoke can be positioned in either upright, inclined or dependent relationship with regard to the surface undergoing test and the strength of the permanent magnets 24, acting through the pole pieces 25, will be sufiicient to hold the: yoke in the position in which it has been placed. By reason of the permanent magnet yoke being self-positioning, the hands of the operator are left free to carry out the operations of the magnetic particle inspection method, as for instance the application of finely divided ferromagnetic powder to the test surface subjected to the magnetic flux of the permanent magnet yoke. Also, because of the sloping nature of the plane end surfaces 45 and their arcuate edges, it is a simple matter to detach the yoke fro: a surface by a rocking movement or by laterally appiied forces against the handle or intermediate portion 11.

It will, of course, be understood that the respective magnets 24, 24 in the permanent magnet yoke assembly so magnetized that the surface 45 of one pole piece will be a North pole and the surface 45 of the other pole piece will be a South pole. The pole pieces, arms 14 and plates 12 and 13 are all formed of soft iron or other relatively permeable ferrous material to give a circuit through the permanent magnet yoke of low flux resistance. While separate pole pieces are not absoiuteiy essential, since the permanent magnets 24 could be so fashioned as to serve as pole pieces, i have found that better utilization of the flux field set up by the permanent magnets can be made if separate pole pieces, as above described, are employed.

in order to prevent unintentional turning of the bolts It and 20, once the desired degree of compression of the spring washers 21 and 22 has been achieved, set screws 50 (Fig. 2) may be threaded in against the shanks of said bolts. In this way the desired resilient resistance to rela tive pivoting movement between the arms 34 and handle 11 is maintained so long as no change in resistance be comes necessary.

It will be understood that modifications and variations may be effected without departing from the-scope 0f the novel concepts of the present invention.

I claim as my invention:

1. A permanent magnet assembly comprising an intermediate portion having bifurcated ends, arms pivotally mounted between said bifurcated ends, means releasably holding said arms in adjusted position relative to said intermediate portion, pole pieces, swivel pins secured in said pole pieces and extending into said arms, means retaining said swivel pins in said arms while permitting relative swivelling movement between said pole pieces and said arms, and resilient means resisting such relative swivelling movement.

2. A permanent magnet assembly comprising an intermediate handle portion, arms pivotally mounted at opposed ends of said handle portion, a pair of magnets, one magnet being disposed at one end of said arms, a pair of pole pieces, one pole piece being secured to each of said magnets, and a pair of swivel pins, each of said swivel pins having one end received tightly in a pole piece to eliminate relative rotational movement therebetween, an intermediate portion extending through one of said magnets, and its opposite end received in one of said arms, and means providing for relative rotational movement between said swivel pin and its associated arm.

References Cited in the file of this patent UNITED STATES PATENTS 1,398,526 Luzy Nov. 29, 1921 2,225,179 Oglevee Dec. 17, 1940 2,501,615 Pugh Mar. 21, 1950 2,575,811 Hofammann et al. Nov. 20, i FOREIGN PATENTS 507,832 Great Britain June 2i, 1939 692,048 Great Britain May 27, 1953 

